The date of the first operation under anesthetic, Oct. 16, 1846, ranks among the most iconic in the history of medicine. It was the moment when Boston, and indeed the United States, first emerged as a world-class center of medical innovation. The room at the heart of Massachusetts General Hospital where the operation took place has been known ever since as the Ether Dome, and the word “anesthesia” itself was coined by the Boston physician and poet Oliver Wendell Holmes to denote the strange new state of suspended consciousness that the city’s physicians had witnessed. The news from Boston swept around the world, and it was recognized within weeks as a moment that had changed medicine forever.

But what precisely was invented that day? Not a chemical – the mysterious substance used by William Morton, the local dentist who performed the procedure, turned out to be simply ether, a volatile solvent that had been in common use for decades. And not the idea of anesthesia – ether, and the anesthetic gas nitrous oxide, had both been thoroughly inhaled and explored. As far back as 1525, the Renaissance physician Paracelsus had recorded that it made chickens “fall asleep, but wake up again after some time without any bad effect,” and that it “extinguishes pain” for the duration.

What the great moment in the Ether Dome really marked was something less tangible but far more significant: a huge cultural shift in the idea of pain. Operating under anesthetic would transform medicine, dramatically expanding the scope of what doctors were able to accomplish. What needed to change first wasn’t the technology – that was long since established – but medicine’s readiness to use it.